<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #d1 {
            width: 100px;
            height: 100px;
            border: 1px solid red;
            /*设置圆角,值越大越圆*/
            border-radius: 100px;
        }
        #d2{
            width: 100px;
            height: 100px;
            border:1px solid red;
            /*给元素添加内边距,默认情况下会改变元素的宽高*/
            padding-left: 30px;
            padding-top: 50px;
            /*添加以下样式后内边距不再影响宽高*/
            box-sizing: border-box;
        }
    </style>
</head>
<body>
<div id="d2">内边距</div>
<div id="d1">边框测试</div>
</body>
</html>